1. Field of the Invention
The present invention relates to a transfer rate controller for controlling a transfer rate when AV data is transferred, a decoding system, a medium, an information aggregate, a recording medium, and a transmitting medium.
2. Related Art of the Invention
In case of performing special reproduction such as cue and review on MPEG image data, only I pictures (intra-coded image) are normally extracted from the MPEG image data, and the extracted I pictures are used as special reproduction data.
The MPEG image data includes P pictures (Predictive coded image), B pictures (Bidirectionally predictive coded image) and so on as well as I pictures.
However, special reproduction data only includes I pictures other than P pictures and B pictures. Further, I pictures are larger in image size than B pictures and P pictures. Therefore, upon reproducing special reproduction image, a larger amount of bits are transferred to a decoder than normal reproduction.
For this reason, a transfer amount to a temporary buffer increases. The temporary buffer temporarily accumulates special reproduction image transmitted to the decoder. Hence, control is necessary for preventing an overflow in the temporary buffer.
FIG. 3 shows a conventional reproducing device 25 that exercise control to prevent an overflow in the temporary buffer during special reproduction.
A reproducing device 25 is configured by a recording means 5, a reproducing means 18, an image data reading means 19, a reading control means 20, a temporary buffer 21, an I/O monitor means 22, a buffer control means 23, and a decoder 11. Moreover, a monitor 4 is connected to the reproducing device 25.
The recording means 5 is a means of recording AV data in MPEG transport stream format. For example, it is possible to use a recording device such as a hard disk being capable of random access and a recording device such as a VCR being capable of sequential access. Hereinafter, the device such as a hard disk being capable of random access will be discussed as a recording means.
The reproducing means 18 is a means of reproducing AV data recorded in the recording means 5. In the case of normal reproduction, the reproducing means 18 outputs reproduced AV data as a PES (Packetized Elementary Stream) in response to request from the image data reading means 19. Also, upon special reproduction, the reproducing means 18 extracts I pictures used for special reproduction from the reproduced AV data, generates special reproduction data, and outputs the data as a PES in response to request from the image data reading means 19.
The image data reading means 19 is a means of reading a PES from the reproducing means 18 according to the control exercised by the reading control means 20, and of outputting the read PES packets as a PES 26 to the temporary buffer 21.
The reading control means 20 is a means of controlling an amount of the PES 26 outputted from the image data reading means 19, based on a state of the input and output of the temporary buffer 21 that is notified of by the I/O monitor means 22.
The temporary buffer 21 is a means of temporarily storing the PES 26 outputted from the image data reading means 19 and of outputting the stored PES 26 to the decoder 11.
The I/O monitor means 22 is a means of monitoring input and output amounts of the temporary buffer 21 and of notifying the reading control means 20 and the buffer control means 23 of the state of the input and output of the temporary buffer 21.
The buffer control means 23 is a means of adjusting an output amount of the temporary buffer 21.
The decoder 11 is a means of decoding a PES transmitted from the temporary buffer 21 and of converting the PES to an analog signal.
The monitor 4 is a means of inputting an analog signal from the decoder 11 and of displaying an image on the monitor 4.
The following will discuss the operation for special reproduction in the conventional reproducing device 25.
The reproducing means 18 reads AV data recorded in MPEG transport stream format in the recording means 5, extracts I pictures used for special reproduction, and converts the extracted I pictures to a PES.
The image data reading means 19 reads the PES according to control exercised by the reading control means 20 and outputs the PES to the temporary buffer 21 as the PES 26.
The temporary buffer 21 temporarily stores the PES 26. And then, the temporary buffer 21 outputs the stored PES for each picture to the encoder 11 according to the control of the buffer control means 23.
The encoder 11 inputs the PES for each picture, decodes the PES, and makes a conversion to an analog signal.
The monitor 4 inputs an analog signal and displays a picture.
Meanwhile, the I/O monitor means 22 monitors an amount of data inputted to the temporary buffer 21 and an amount of data outputted from the temporary buffer 21 to the decoder 11.
And then, the reading control means 20 and the buffer control means 23 is notified of a state of the input and output of the temporary buffer 21.
The reading control means 20 always monitors information from the buffer monitor means 22 and exercises control such that the image data reading means 19 reads data for special reproduction in PES format when the temporary buffer 21 outputs data to the decoder 11. Subsequently, the image data reading means 19 stores the read data in the temporary buffer 21.
Further, the buffer control means 23 always monitors information from the buffer monitor means 22 and exercises control such that data of one picture is outputted to the decoder 11 when data of one picture is stored in the temporary buffer 21.
As described above, the reading control means 20 and the buffer control means 23 control the input and output of a PES of the temporary buffer 21, according to the state of the input and output of the temporary buffer 21 that is transmitted from the I/O monitor means 22.
Therefore, the data input to the temporary buffer 21 and the data output from the temporary buffer 21 are controlled in synchronization with each other, thereby preventing an overflow in the temporary buffer 21.
Incidentally, the following will discuss a system in which functions for reproducing AV data and decoding the reproduced AV data are separately realized by different devices and the AV data reproduced in the reproducing device is transferred to a decoding system as an MPEG transport stream.
FIG. 4 shows such a system.
A reproducing device 27 is a device for reproducing AV data and outputting it as an MPEG transport stream. Moreover, a decoding system 28 is a device for decoding the AV data transmitted as an MPEG transport stream and displaying its picture on the monitor 4.
For example, an IEEE 1394 bus connects the reproducing device 27 and a decoding system 28.
The reproducing device 27 is configured by a recording means 5, a reproducing means 6, an image data reading means 7, and a reading control means 20.
Further, the decoding system 28 is configured by a converting means 29, a temporary buffer 9, a decoder 11, an I/O monitor means 22, and a buffer control means 23.
The reading means 5 and the reading control means 20 constituting the reproducing device 27 are identical to those of FIG. 3.
Additionally, unlike the reproducing means 18 of FIG. 3, the reproducing means 6 is a means of outputting generated special reproduction data as an MPEG transport stream.
Unlike the image data reading means 19 of FIG. 3, the image data reading means 7 is a means of reading an MPEG transport stream and outputting it as an MPEG-TS (MPEG transport stream) 12.
The I/O monitor means 22, the buffer control means 23, a temporary buffer 9, and the decoder 11 constituting the decoding system 28 are identical to those of FIG. 3.
Additionally, the converting means 29 is a means of inputting a transmitted MPEG transport stream, making a conversion to a PES, and outputting the PES.
The following will discuss the operation for special reproduction in the reproducing device 27 and the decoding system 28 as configured above.
The reproducing means 6 reads AV data recorded in MPEG transport stream format in the recording means 5 and extracts I pictures used for special reproduction. And then, the reproducing means 6 outputs the extracted I pictures as an MPEG transport stream.
The image data reading means 7 reads the MPEG transport stream and outputs it to the converting means 29 as the MPEG-TS12 via an IEEE 1394 bus.
The converting means 29 converts the MPEG-TS12 transmitted from the reproducing device 27 to a PES and outputs it to the temporary buffer 9.
The temporary buffer 9 temporarily stores the PES. And then, the temporary buffer 9 outputs the stored PES for each picture to the decoder 11 according to the control of the buffer control means 23.
The decoder 11 input the PES for each picture, decodes it, and makes a conversion to an analog signal.
The monitor 4 inputs the analog signal and displays a picture.
Meanwhile, the I/O monitor means 22 monitors an amount of data inputted in PES format to the temporary buffer 9 and an amount of data outputted in PES format from the temporary buffer 9 to the decoder 11.
Meanwhile, the I/O monitor means 22 notifies the buffer control means 23 of the state of the input and output of the temporary buffer 21.
However, the reproducing device 27 and the decoding system 28 are connected with each other via an IEEE 1394 bus and so on. Hence, unlike the configuration of FIG. 3, the I/O monitor means 22 cannot notify the reading control means 20 of detailed information such as a state of the input and output of the buffer 21 without delay.
Moreover, the image reading means 7 outputs AV data in MPEG transport stream format, so that an amount of the output cannot be changed freely.
Therefore, in the configuration of FIG. 4, upon special reproduction, it is not possible to synchronize an input amount and an output amount of the temporary buffer 9, so that an overflow may occur in the temporary buffer 9.
As described above, when the devices are configured separately for reading AV data and decoding the read AV data, it is difficult for the reading device to know the state of the buffer. The buffer temporarily stores data transmitted to the decoder.
Also, even if the state of the buffer is known to the reading device, when AV data is transferred as an MPEG transport stream from the reading device to the decoding system, an amount of transfer cannot be adjusted freely. For this reason, an overflow may occur in the buffer.
Namely, in the case where the devices are configured separately for reading AV data and decoding the read AV data, the buffer for temporarily storing data transmitted to the decoder may have an overflow during special reproduction.